MarkWest Energy Partners and its subsidiary, MarkWest Energy Finance, will offer an additional $200 million of 6.5% senior unsecured notes maturing in 2021. MarkWest had previously sold $300 million of the 6.5% notes on Feb. 24, 2011.

The proceeds from the additional note offering will be used to acquire about $165.5 million of its 8.75% senior notes, due in 2018. The additional notes and the previously issued notes will be treated as a single class of debt securities under the indenture.

Click here for the release from Business Wire.